The present invention relates to a developing unit usable with and removably mounted on a copier, printer, facsimile machine or similar image recording apparatus.
Many of image recording apparatuses of the type described such as copiers available today are designed for personal use. A current trend in the field of personal copiers is toward the construction of various replaceable parts into a unit which would promote the replacement by users instead of servicemen. However, a problem with a developing unit, for example, is that various replaceable parts including the body of the unit and a developer which is expendable have to be replaced altogether despite that the service life differs from one part to another. Discarding even those parts which are still usable increases the running cost per copy. In the light of this, there has been proposed a system which combines a plurality of cartridges with a single developing unit and determines that the life of the unit has expired when a predetrmined number of cartridges have been successively used and emptied. For example, Japanese Patent Laid-Open Publication (Kokai) Nos. 87464/1984 and 124052/1986 each discloses a developing unit having a developing roller and a toner cartridge and counting toner cartridges which are loaded in the unit one after another. After the developing unit has been operated with a predetermined number of successive toner cartridges, any other toner cartridge is inhibited from being located in the unit. Japanese Patent Laid-Open Publication No. 75756/1988 proposes a developing unit which is loaded with a plurality of toner cartridges one at a time in a predetermined order and, when loaded with the last toner cartridge, does not allow it from being removed later and thereby inhibits the use of new cartridges.
The prior art schemes discussed above have a drawback that when the user supplies a toner without using a cartridge, i.e., by using a spoon or the like, a counter associated with a developing unit does not function at all. Then, the actual state of use of the developing unit fails to coincide with the life of the unit being displayed, resulting in machine troubles and unusual images.
A color copier for personal use is also extensively used which is selectively operable with some developing units each being loaded with a developer of different color. Generally, such developing units each has a developing section and a toner storing section which are formed integrally with each other. When the copying operation has been executed with any one of such developing units a number of times which matches the amount of toner stored therein, the developing unit is bodily replaced with another.
However, with the conventional system stated above, it is impossible for the user to clearly see if the individual developing units are still usable. Specifically, the user cannot see if a defect occurs in an image unless the user actually mounts desired one of the developing units on the apparatus body.